he 2009 outbreak of influenza A (H1N1) virus is an epidemic of a new strain of influenza virus that was clinically identified in April 2009,[35] and is commonly referred to as swine flu.[36] It is currently a Phase 5 outbreak, one level below an official pandemic.
Although the exact origin of the outbreak is unknown, it was first detected when officials in Mexico and the United States suspected a link between an outbreak of late-season flu cases in Mexico and cases of influenza in Texas and California.[37] Within days, hundreds more suspected cases were discovered in Mexico, with more cases also showing up in the U.S. and several other countries.
By late April, officials from the U.N.'s World Health Organization (WHO), based in Switzerland, and the Centers for Disease Control and Prevention (CDC) in the U.S., were expressing serious concern about the flu outbreak, worried that it might become a worldwide flu pandemic.[38] As a result, WHO raised its alert level to "Phase 5" out of 6 possible, which it defines as a "signal that a pandemic is imminent".[39]
By the end of April 2009, governments across the world had taken emergency measures to slow the transmission of a possible pandemic.[40] At the same time, however, many scientists were reaching a consensus that the "epidemic" which until May 6 has had fewer than 31 deaths confirmed worldwide, was so far relatively "extremely mild" and believed that it could be less fatal than previous pandemics. [41]
The new strain is an apparent reassortment of four strains of influenza A virus subtype H1N1.[42] Analysis by the CDC identified the four component strains as one endemic in humans, one endemic in birds, and two endemic in pigs (swine).[42] However, other scientists have stated that analysis of the 2009 swine flu (A/H1N1) viral genome suggests that all RNA segments are of swine origin,[43] and "this preliminary analysis suggests at least two swine ancestors to the current H1N1, one of them related to the triple reassortant viruses isolated in North America in 1998."[44] One swine influenza strain was widespread in the United States, the other in Eurasia.[42]
Worldwide the common human H1N1 influenza virus affects millions of people every year, according to WHO officials, and "these annual epidemics result in about three to five million cases of severe illness, and about 250,000 to 500,000 deaths" annually.[45] In industrialized countries most of these annual deaths occur in people aged 65 or older.[45] By May 2, some pigs in Canada were diagnosed with H1N1.[46] Although some influenza strains can spread between species, the influenza virus is killed by normal cooking procedures, so there is no risk of infection from consumption of well-cooked pork and pork products.[47]
